In commercial and off-the-road vehicles, wheel assemblies having dual pneumatic tires are commonly used, with typically a set of dual tires mounted on each end of an axle. During normal operation of such a vehicle the air pressure in the dual tires may not be equal. This can be caused by improper inflation, uneven heating of the tires, or an air leak in either tire. Correct and properly balanced pressure in the dual tires will help to provide even wear and longer life of the expensive tires. Numerous innovations for equalizing dual tire pressure have been provided in prior arts but few covered dual tire pressure monitoring. Some innovations are related to dual tires equalizer with a simple mechanical pressure indicator. For direct pressure monitoring, electronic pressure sensors have long been used to monitor tires for determining whether the tire was properly pressurized. However most related prior inventions for tire pressure sensors were for single tire pressure monitoring only. Numerous innovations for inflating dual tires also have been provided but few covered controlling tire inflation with real-time dual tire pressure measurements.
U.S. Pat. No. 4,539,928 issued to Gordon R. Todhunter on Sep. 10, 1985 discloses a tire equalizer device that comprises a housing having upper and lower chambers divided by a flexible diaphragm opposing a seat in the upper chamber connected to one of the tires. The diaphragm is urged toward the seat by a spring-pressed inverted cup larger in diameter than the diaphragm and having an arm extended longitudinally from the cup away from the spring. The arm is curved in horizontal cross-section and its upper end is formed with a slot receiving an off-center pin on the back of an indicator disc. Also connected to the upper chamber is a fill conduit, and a conduit to the other tire.
U.S. Pat. No. 5,302,939 issued to Edward A. Downs on Apr. 12, 1994 discloses a dual tire equalizer having a diaphragm that pushes a spring-loaded rod between two switch devices which, when the tire is not properly pressurized, will trigger the sending of an encoded RF signal to a receiver for generating alarms.
U.S. Pat. No. 5,302,939 issued to Edward A. Downs on Apr. 12, 1994 discloses a method and apparatus for maintaining equal air pressure in a dual tire. The invention provides a valve body with a pair of piston chambers.
U.S. Pat. No. 7,656,281 issued to Joe Huayue Zhou on Feb. 2, 2010 discloses an external valve stem mounted tire pressure monitoring sensor with air flow through feature. Particularly, the invention relates to an apparatus of a miniature external valve stem mounted tire pressure sensor design that allows refilling tire air through the sensor built-in valve stem without needing to remove the sensor, and methods for constructing and operating the apparatus.
Typically, these systems teach equalizing dual tires without continuous pressure monitoring and remote notification, or only do tire pressure monitoring without dual tire equalizing. Furthermore, these teachings do not address or not able to resolve many practical issues, as described below:
(i) Dual Tire Pressure Monitor with Equalizer Function
Properly pressurized and equalized tires in a dual tire set are utmost important for safe driving and for prolonging the life of tires. However prior tire pressure monitoring systems (TPMS) generally only monitor tires without pressure equalization and, therefore, can only be used as a separate system to support tire monitoring for the dual tire pressure equalizing systems. It is technically challenging to make a small, integrated dual tire pressure monitor with equalizer that can monitor individual tire pressure in a dual tire set, refill air without removing the sensor, and equalize the pressure in the two tires. Prior teachings generally do not present practical methods to make small external dual tire sensors with pressure equalizer.
(ii) Dual Tire Pressure Monitor with Equalizer and Tire Inflation System Integration
There are many tire inflating systems available on the market and most of them are designed for trailer installation. Such systems use compressed air from the trailer air tank to inflate tires having pressure that fell below a preset level. Air from the existing trailer air supply is routed to a control box and then fed into air tubes installed inside each axle. The air tubes run through the axles to carry air through a rotary union assembly joined at the wheel spindle end in order to distribute air to each tire.
Although good tires usually able to keep proper pressure for weeks, a tire inflation system on a vehicle often must operate every trip due to possible air line and seal leaks. In addition, tire inflation systems generally do not have direct pressure readings from the dual tires for controlling the inflation and, therefore, must inflate from time to time and check if the preset pressure was maintained on the air line. If pressure was still low after a period of time then the systems would deduce that there might be a leaky or flat tire. This indirect detection of air leak and flat tire is unreliable and usually belated, and the excessive work load putting on the rotary hub seal unit and the air compressor will wear out the parts sooner and would lead to more expensive vehicle maintenance and even unsafe driving conditions. A tire inflation system integrated with tire pressure monitor and equalizer would have accurate inflation control based on real-time tire pressure data and, as a result, works less and thereby reduces the vehicle maintenance costs; most importantly such an integrated system improves vehicle safety for it would be able to notify the driver low or flat tire condition immediately.
A tire inflation system integrated with a direct tire pressure monitor, even without the pressure equalizing function, can also provide substantial benefits in accurate inflation control, improved vehicle safety, and system maintenance cost reductions.